- Type THHN or THWN-2* conductors are primarily used in conduit and cable trays for services, feeders, and branch circuits in commercial or industrial applications as specified in the National Electrical Code2.
- When used as Type THHN, conductor is suitable for use in dry locations at temperatures not to exceed 90°C.
- When used as Type THWN-2*, conductor is suitable for use in wet or dry locations at temperatures not to exceed 90°C or not to exceed 75°C when exposed to oil or coolant.
- When used as Type MTW, conductor is suitable for use in wet locations or when exposed to oil or coolant at temperatures not to exceed 60°C or dry locations at temperatures not to exceed 90°C (with ampacity limited to that for 75°C conductor temperature per NFPA 79).
- Conductor temperatures not to exceed 105°C in dry locations when rated AWM and used as appliance wiring material. Voltage for all applications is 600 volts.
Standards: THHN or THWN-2* or MTW (also AWM) meets or exceeds all applicable ASTM specifications
- UL Standard 83
- UL Standard 1063 (MTW)
- Federal Specification
- A-A-59544, and requirements of the National Electrical Code.
Frequently Asked Questions - THHN THWN-2 Copper Conductor Building Wire
What does “THHN” and “THWN” stand for?
- T - Stands for Thermoplastic insulation.
- HH – Has a higherheat resistance
- N – Indicates that the wire is nylon coated. Copper wires that are stranded and solid can have a mechanical coating of nylon which protects them from oil and gas.
- H – A single H just indicated that it is resistant to heat but it cannot match the resistance that is given by HH.
- W – It is resistant to water and moisture. So it can be used in both wet and dry locations.
What is the maximum working temperature for THHN THWN-2 Copper Conductor Building Wire?
You can use the wire up to a temperature of 90°C when used as a Type THHN. The maximum temperature for Type THWN-2 is also 90°C. However, when the wire is used in industries where it can be exposed to oil or coolant, then care must be taken to ensure that the maximum working temperature is 75°C or below.
How is the THHN THWN-2 Copper Conductor Building Wire constructed?
The copper conductorsare made with soft annealed copper, which are insulated with PVC insulation. This makes the conductors resistant to extreme heat and moisture. Then there is an overall jacket that has a nylon jacket.
Where can you use the THHN THWN-2 Copper Conductor Building Wire?
You can use the conductor for all types of services and feeders in both commercial and industrial applications. The conductor is also ideal for use in branch circuits in conduit and cable trays. When used as a Type THWN-2, it can be used in both wet and dry locations.
What are the standards and references that are met by the THHN THWN-2 Copper Conductor Building Wire?
The Type THHN and THWN meet the following specifications –
- UL Standard 83
- Federal Specification A-A-59544
- National Electrical Code
Can I use the Type THHN THWN-2 Copper Conductor Wire for lamp posts instead of a UF wire?
Ideally, people use a UF wire for lamp posts, but you can also use the Type THHN THWN-2 for it. You can just run it inside the lamp post but you must have a conduit. The conduit must come above the ground either inside the lamp post itself or next to it. Also, please note that underground conduits are considered as wet locations. So you will have to use a splice method suitable for wet locations even if the conduit is dry.